Fuel system valves, located in airplane fuel tanks, allow the transfer of aviation fuel from the tanks to the engines. Fuel tanks may be located in the fuselage, in the wings, and in other locations on the plane. Typically, electrically operated actuator drive shafts are used to drive the fuel system valves in airplanes. These actuator drive shafts are manufactured from electrically conductive metallic materials. The metallic drive shafts allow the possibility, under certain conditions, that electrical current may pass through them and into the fuel tank, resulting in an ignition source.
Various devices to protect airplane fuel tanks against sparking have been developed.
U.S. Pat. No. 4,971,268 issued to Dobrowski et al. is concerned with preventing sparking caused by tubing within a fuel tank. It uses a sleeve having sufficiently high dielectric strength to prevent electrical arcing between the tubing and any immediately adjacent structure.
U.S. Pat. No. 5,709,356 issued to Avenet et al. discloses an anti-spark structure including two elements of composite material. The structure forms part of an aircraft's fuel tank. A metal screw is placed within the two elements of composite material. When lightning reaches the head of the screw, the current passes into the two elements. Gasses created by heating due to the current flow are removed toward the outside of the anti-spark structure through a passage within the screw.
U.S. Pat. No. 6,141,194 issued to Maier discloses an aircraft fuel tank protective barrier which includes a transformer. The transformer limits an amount of energy delivered to the fuel tank in the event of a fault experienced on the wiring. The core saturation of the transformer is utilized to limit the energy transfer to the tank during power fault conditions while the common-mode rejection of the transformer is used to block lightning strikes.
U.S. Pat. No. 6,343,465 issued to Martinov discloses ducting, one end of which is in communication with the aircraft's fuel tank and the other end is coupled to the engine air intake area. The operating engine's intake suction force is used to drive the system of purging and removing dangerous fumes and heat from the fuel tank areas and conducts them into the engine's combustion chamber areas for combustion and exhaust. The removed fumes and heat are replaced by ambient outside air, mechanically refrigerated air or cabin-cockpit overflow air through the tank intake valves.